Dry heat sterilization is one of the most practical and preferable forms of sterilization, using blown hot air to eliminate or deactivate all forms of life inside the chamber of an industrial oven.
Dry heat was actually one of the very first methods of sterilization, has highly predictable results, and can be modified to suit a wide range of different sterilization requirements.
How Dry-Heat Sterilization Works
Dry air is blown onto the object that is to be sterilized, passing energy to it through conduction (forced air). Alternatively, an oven could use heated coils instead of fans (static air), but the forced air type is preferable as it delivers the heat load to the object with better homogeneity.
Typically, the setting must be at 160 °C (320 °F) for a duration of two hours, 170 °C (340 °F) for one hour, and up to 190°C (375°F) for 6 to 12 minutes. These are typical cycle times, and depending on the specific application, they may be set differently. Depending on the oven type and the blower unit that is used, the times for the achievement of sterilization vary. For example, some ovens deploy high-velocity blowers with multiple and powerful fans, delivering large volumes of hot air onto the object. Consider the cycle times of these to be half of what is presented above for conventional air circulation capacities.
The heat that is passed onto the object is causing the denaturation of proteins on all bacterial spores, fungi, viruses, prions, and generally all forms of biological agents. Denaturation is the deconstruction of nucleic acids, so all living cells essentially die from energy starvation, whereas viruses are permanently deactivated due to extensive damage on their encoding RNA or DNA. Removing all moisture from the air that is blown inside the oven chamber is imperative, as this moisture can interfere with the protein denaturation process.
Moist heat sterilization is a different process altogether, used for a separate set of applications and sterilization purposes.
Advantages of Dry-Heat Sterilization:
- Dry heat ovens are generally cheap to buy.
- The cost of operation and heating cycles is generally low.
- The heat can go deeply into thick objects, achieving an in-depth sterilization effect. Even objects inside packaging can be sterilized this way.
- Metallic objects that can handle heat well can be sterilized quickly at high temperatures.
- Dry heat is non-corrosive for metallic materials as it contains too little moisture.
- The process involves no toxic agents, so there are no harmful substances that will be discarded in the environment.
- Requires no human attendance or intervention during operation. Someone has to set the oven and leave it to complete the cycle.
- The object can be taken out and used almost immediately, as it cools down quickly.
Disadvantages Compared to Other Processes
- The dry heat can take much more time to achieve sterilization than what is required with steam, flaming, chemical sterilization, or radiation.
- The heat can cause warping to sensitive materials or thin sheets.
- The high temperatures can irreversibly damage plastics, rubber, so these are not suitable for dry heat.
- Overexposure to heat even for materials that can handle it can result in unwanted changes in the chemical structure of some substances.
Common Applications of Dry Heat Sterilization
There is a wide range of materials that can handle dry heat well, and that is why this method is so popular and widely used. Examples include metals of all kinds, powders that can’t be compromised by moisture or chemical agents, anhydrous oils and fats, and glassware. Moreover, and because dry heat can penetrate objects so well, paper-wrapped items can be sterilized effectively, as can medical instruments of intricate geometry such as syringes (metal and glass) or surgical tools.
Despatch offers a wide selection of sterilizing ovens that feature a variety of chamber sizes and temperature capabilities. If you need more information about any of our ovens, from oven design, sales to installation and maintenance services, please contact us.